JP3191276B2 - Runnerless mold - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a runnerless mold used for injection molding of a thermoplastic resin.

[0002]

2. Description of the Related Art Conventional runnerless dies include a valve gate type and a hot tip type.
In these molds, the gate is in the fixed mold, and opens to the cavity along the opening and closing directions of the fixed mold and the movable mold. In the mold of the valve gate system, the gate is mechanically opened and closed by the valve pin moving in the opening and closing direction, and in the mold of the hot chip system, the resin in the gate portion is melted by controlling the heating by the hot chip, The gate is opened and closed by solidification.

Incidentally, in these molds, the gate is often opened to a position corresponding to the front of the product in the cavity. However, in some cases, it is not preferable to form a gate mark on the front of the product due to the appearance of the product. In such a case, the gate is opened at a position corresponding to the side surface of the product in the cavity. Since the side surface of the product is along the mold opening / closing direction, a side gate as shown in FIG. 4, for example, is used as the gate.

In FIG. 4 showing a conventional mold, 1 is a fixed mold, 2 is a movable mold, and these fixed mold 1 and movable mold 2 are
The molds are moved vertically in the figure to open and close, and a plurality of product-shaped cavities 3 are formed therebetween when the mold is closed.
The cavity 3 is set so that the front part A1 of the product A is orthogonal to the mold opening and closing direction (vertical direction in the drawing), and the side part A2 is substantially along the mold opening and closing direction. Although not shown, the fixed mold 1 is connected to a nozzle of an injection molding machine, and has a manifold for distributing the molten resin injected from the nozzle to each cavity 3. This manifold has a heater to keep the resin inside in a molten state at all times. Further, the fixed mold 1 has a sub-sprue 4 communicating with a runner of the manifold, and a hot chip 5 having a built-in heater is provided in the sub-sprue 4. Further, when the mold is closed, a sub-runner 7 is formed between the fixed mold 1 and the movable mold 2 so as to communicate with the primary gate 6 at the tip of the sub-sprue 4.
, A side gate 8 is formed which opens to a position corresponding to the side surface portion A2 of the product A in the cavity 3. further,
The movable die 2 is provided with protrusion pins 9 and 10 that move up and down so as to face the cavity 3 and the sub-runner 7, respectively.

At the time of molding, the molten resin is filled from the sub-sprue 4 into the cavity 3 through the primary gate 6, the sub-runner 7 and the side gate 8 with the mold closed. After that, the hot tip 5
By controlling the heater inside, the resin in the primary gate 6 is cooled and solidified. Note that the resin in the sub-sprue 4 is always kept in a molten state by heating the heater.
Further, after the resin in the cavity 3 and the sub-runner 7 is sufficiently cooled and solidified, the mold is opened. At this time, the resin solidified in the cavity 3, that is, the resin solidified in the product A and the sub-runner 7 (hereinafter referred to as “runner resin”)
B first moves away from the fixed mold 1, and then is protruded upward by the protruding pins 9, 10 to move away from the movable mold 2.

[0006]

However, the conventional mold as shown in FIG. 4 has the following problems because the sub-runner 7 is a cold runner. First,
The product A and the runner resin B must be cut by post-processing after molding, and this gate processing increases man-hours. Further, the runner resin B is wasted and is not economical.

The present invention is intended to solve such a problem. In spite of the fact that the gate is opened to the cavity from a direction intersecting with the mold opening and closing direction, waste of resin can be eliminated, and the gate can be eliminated. It is an object of the present invention to provide a runner-less mold that does not need to be subjected to post-processing after molding and can increase the productivity of molding itself.

[0008]

In order to achieve the above object, a runnerless mold according to the present invention has a first mold and a second mold which open and close with each other and form a cavity therebetween when the mold is closed.
A first resin passage heated by a heater and a side surface extending in a direction intersecting with the opening and closing direction of the two molds in the first mold body. Forming a second resin passage communicating with the gate through the gate and having a tip opening to the cavity as a second gate;
A valve pin slidably fitted in the second resin passage, and the valve pin being moved between a position where the tip is on the opposite side of the cavity from the first gate and a position where the valve pin is located on the second gate. And a driving device for moving the object.

[0009]

In the runnerless mold of the present invention, the first
The mold body and the second mold body are closed, and at the same time, the tip of the valve pin is first positioned by the driving device on the side opposite to the cavity from the first gate. In this state, the first resin passage communicates with the cavity via the first gate, the second resin passage, and the second gate. Then, the molten thermoplastic resin is filled from the first resin passage into the cavity through the first gate, the second resin passage, and the second gate. After this filling, the cavity and the second
Before the resin in the resin passage is solidified,
The valve pin is advanced toward the second gate. The valve pin slides in the second resin passage, closes the first gate, pushes the resin in the second resin passage into the cavity, and finally reaches the second gate. . By the advance of the valve pin, the pressure in the resin in the cavity is maintained, and the gate processing is performed. Further, after the resin in the cavity is sufficiently cooled and solidified, the mold is opened and the molded product is taken out. Note that the resin in the first resin passage is always kept in a molten state by the heating of the heater.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a runnerless mold according to the present invention will be described below with reference to FIGS. In FIG. 1, reference numeral 21 denotes a fixed mold as a first mold, and 22 denotes a second mold.
The fixed mold 21 and the movable mold
Numerals 22 move upward and downward in the figure to open and close, and form a plurality of product-shaped cavities 23 therebetween when the mold is closed. The cavity 23 is set so that the front part A1 of the product A is orthogonal to the mold opening / closing direction (vertical direction in the drawing), and the side part A2 is substantially along the mold opening / closing direction.

Although not shown, the fixed die 22 is connected to a nozzle of an injection molding machine, and has a manifold for distributing the molten resin injected from the nozzle to the cavities 23. This manifold has a heater to keep the resin inside in a molten state at all times. In the fixed mold 21, a sub-sprue 24 is formed as a first resin passage communicating with the final branch of the runner of the manifold. A hot chip 25 having a built-in heater is provided in the sub-sprue 24. ing. At the same time, a cylindrical sub-runner 26 as a second resin passage is formed in the fixed mold 21 perpendicular to the mold opening and closing direction. A first gate 27 at the tip (the lower end in the figure) of the sub sprue 24 is opened on the upper side surface of the sub runner 26. The tip of the sub- runner 26 is a second gate 28 that opens to the cavity 23. And
A cylindrical valve pin 31 having substantially the same diameter as the sub- runner 26 is slidably fitted in the sub- runner 26 in the axial direction.
The fixed mold 21 is provided with a hydraulic cylinder 32 as a driving means for moving the valve pin 31. The moving range of the valve pin 31 is, as shown in FIG. 1A, a position where the tip is on the side opposite to the cavity 23 with respect to the first gate 27, and as shown in FIG. Gate of
It is between the positions at 28. At this time, the tip of the valve pin 31 coincides with the outer surface of the side part A2 of the molded product A.

The movable die 22 is provided with a projecting pin 36 that moves up and down so as to face the cavity 23.

Next, the operation of the above configuration will be described. At the time of molding, the fixed mold 21 and the movable mold 22 are closed and, as shown in FIG.
With 32, the valve pin 31 is positioned at the retreat limit. In this state, the sub sprue 24 communicates with the cavity 23 via the first gate 27, the sub-runner 26, and the second gate 28. Then, by the injection operation of the injection molding machine, the molten thermoplastic resin is supplied from the sub sprue 24 to the first gate 2.
7. The cavity 23 is filled through the sub-runner 26 and the second gate 28. After the filling, before the resin in the cavity 23 and the sub-runner 26 solidifies, the valve pin 31 is moved to the second gate 28 by driving the hydraulic cylinder 32.
Advance towards. The valve pin 31 slides in the sub-runner 26, first closes the first gate 27, and pushes the resin in the sub-runner 26 into the cavity 23, while the tip finally reaches the second gate 28. . This valve pin
With the advance of 31, the pressure in the resin in the cavity 23 is maintained, and the gate processing is also performed. Further, the resin in the cavity 23 is sufficiently cooled,
After solidification, the mold is opened. At this time, cavity 3
The resin solidified therein, that is, the product A is first separated from the fixed mold 21 and then protruded upward by the protruding pin 36, separated from the movable mold 22 and taken out. Thereafter, the mold is closed again and the molding is repeated. The resin in the sub sprue 24 is always kept in a molten state by the heating of the hot chip 25.

As described above, according to the configuration of the above embodiment, although the gate 28 is opened at the position corresponding to the side A2 of the product A in the cavity 23, the gate 28 is provided at the tip. Valve pin 31 in sub-runner 26
Is provided, gate processing can be performed at the time of molding, and it is not necessary to perform gate processing in post-processing, and a complete runner-less mold can be obtained, thereby eliminating waste of resin. Moreover, after filling the cavity 23 with the resin, the valve pin 31 is advanced to close the first gate 27, and thereafter, the pressure is maintained by the valve pin 31. Therefore, in the injection molding machine, the pressure is maintained after the injection. The metering can be started immediately without any control, and the productivity of the molding itself can be increased. Further, since the first gate 27 is closed by the valve pin 32,
Control of the hot tip 25 is also simplified.

It is necessary to adjust the stroke of the valve pin 31 and the injection amount of the injection molding machine so that proper molding including holding pressure is performed. This can be determined as usual, from the first trial, while observing the results. During the pressure holding, the resin in the sub-runner 26 is pushed into the cavity 23, and the adjustment of the resin amount for the proper pressure holding is performed by adjusting the position of the valve pin 31 in the retreat limit. Then, the injection amount from the injection molding machine is adjusted accordingly.

In addition, as for the position of the valve pin 31 in the advance limit, if the tip of the valve pin 31 is made to coincide with the outer surface of the side surface portion A2 of the formed product A, the gate mark on the product A is less noticeable. Good. Further, it is possible to make the tip of the valve pin 31 slightly protrude into the cavity 23. In this case, as it is, the valve pin 31
After the product A has sufficiently solidified, the valve pin 31 may be retracted and removed from the product A before the mold is opened. On the other hand, the fact that the tip of the valve pin 31 does not reach the cavity 23 in the forward limit is not possible because the product A has an undercut that hinders release.

Further, the present invention is not limited to the above embodiment, and various modifications can be made. For example, the cross-sectional shape of the valve pin 31 is not limited to a circular shape as shown in FIG. 2, but may be a rectangular shape as shown in FIG. Further, the driving device of the valve pin is not limited to the hydraulic cylinder.

[0018]

According to the present invention, in a mold in which a gate is opened to a cavity from a direction intersecting the opening / closing direction of a pair of molds, a first resin passage heated by a heater is provided in the first mold. A second resin passage communicating with the side surface via the first gate and having a tip serving as a second gate to the cavity, and a valve pin fitted in the second resin passage; Since a driving device is provided for moving the valve pin between a position where the tip is on the side opposite to the cavity from the first gate and a position where the valve pin is located on the second gate, after filling the cavity with the resin, Before it solidifies,
By advancing the valve pin to the second gate,
Gate processing can be performed at the same time as molding, and there is no need to perform gate processing in post-processing, and no solidified resin other than the product is generated, and waste of resin is eliminated. Further, since the pressure in the resin in the cavity can be maintained by the valve pin, in the injection molding machine, the measurement can be started immediately without performing the pressure maintenance control after the injection, and the productivity of the molding itself can be increased.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view showing one embodiment of a runnerless mold of the present invention.

FIG. 2 is a front view of the valve pin.

FIG. 3 is a front view of a valve pin showing another embodiment of the present invention.

FIG. 4 is a partial cross-sectional view showing an example of a conventional mold.

[Explanation of symbols]

 21 Fixed mold (first mold) 22 Movable mold (second mold) 23 Cavity 24 Sub sprue (first resin passage) 26 Subrunner (second resin passage) 27 First gate 28 Second Gate 31 Valve pin 32 Hydraulic cylinder (drive unit)

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B29C 45/26-45/44

Claims (1)

(57) [Claims] 1. A first resin body having a first mold body and a second mold body which open and close with each other and form a cavity therebetween when the mold is closed, and a first resin passage heated by a heater in the first mold body. And a second resin passage having a side surface extending in a direction intersecting the opening and closing direction of the two molds and communicating with the first resin passage via a first gate, and a tip opening to the cavity as a second gate. And a valve pin slidably fitted in the second resin passage, and a valve pin having a tip located on the opposite side of the cavity from the first gate and the second gate. A runner-less mold provided with a driving device for moving the mold to and from a certain position.